Radio navigation



Mav'rch'vZ,"19375.. w, ALBERSHEIM v-|=:r AL 1,995,285

RADIO NAVIGATION Filed Jan. 25, 1929 We O )www abme/l Patented Mar. 26,1935 RADIO NAVIGATION Walter Albersheim and Harvey Konhelm, New York, N.Y.

Applicatin January z5,

11 Claims.

'Ihis invention relates to an aeronautical navigation method and means,We are aware that radio-beam beacons have been employed as a means toguide an air-ship in its flight; and also that it has been proposed touse directional loops as a means to determine the position of a ship inflight.

It is an object of this invention to provide a method and means formeasuring the speed of travel of a ship in the air with respect to theground.

It is a further object of this invention to provide a method andmeansfor determining the position of a'ship in flight.

Further, it is an object of this invention to provide a method and meansfor determining the magnitude and direction of wind drift as it effectsa ship in flight.

Briefly, the objects of our invention are accomplished as follows:

Continuous wave oscillations of equal frequencies are broadcast'simultaneously from twov transmitters placed at separate fixed points.It will be demonstrated mathematically, that a ship having two separatereceivers, each of which is adjusted to receive one of the saidbroadcastv waves, and both receivers arranged to feed into a commonmixing tube, will produce a beat note, which beat note is due to themotioncf the ship in the common .field of the transmitters and thefrequency of said beat is a known function of the location and directionof travel of the ship.v

In actual'practice the beat note thus produced is below audibility, andwe havetherefore devised a circuit which will enable such frequency tobe indicated visually.

Having determined the frequency of the beat note, in accordance with theprinciples of .this invention the location of the ship, direction offlight and wind drift may be readily determined.

, The mannerin which our invention is carried out will more clearlyappear from the following description taken in connection with theaccompanying drawing in which:

Fig..1 is a diagrammatic representation of a receiving apparatus used inaccordance with this invention; and

Figs. 2-8 are diagrams used in explaining the principles. of thisinvention.

Two separate transmitters are located at the points A andB, Figs. 4--7,for ecample, each of the transmitters operating in .unison that is, onidentical frequencies. Means for,` broadcasting oscillations onidentical frequencies, or on frequencies one ofwhich is an integralmultiple of Vcontinuous wave with a musical note having a 1929, SerialNo. 335,087

` (Cl. Z50-2) the other, are well known in the art. Therefore, we shalldescribe below only briefly the principle preferably used in accordancewith our invention for such broadcasting. A

A first station indicated as A (see Figs. .4-7) broadcasts a continuouswave of a high frequency, for example, 15 megacycles. Preferably thiscontinuous wave is modulated to a small percentageby a xed musical notehaving a frequency of 400 cycles per second, for'example. 10 However,such modulation serves merely as an aid to the identification of thestation A, and may be omitted without departing from the spirit of thisinvention. Another advantage of using this modulation by an audiofrequency resides in the 15 fact that the modulated continuous wave maythen be used for the transmission of code messages.

Station B (seeFigs. 4 7) receives this signal transmitted by A, filtersout the modulated fre- 20 quency and amplii'les it. This received signalfrom A then serves as master oscillation for the transmitter of B, whichis thereby bound to broadcast in unison with A. Precaution must be takento prevent the output of the B transmitter from feeding back into thereceiver and causing self-sustained oscillations in the transf mitter ofB independent of As signal. Station B may also modulate a smallpercentage of this frequency of, for example, 500 cycles per second forthe purposes of identification and the transmission of code messages.

A desirable modication of this method consists in passing the signalreceived in B through a frequency multiplier, the output of which servesas master oscillation for the transmitter. Station B will thus broadcaston a harmonic of As wave. This will make it easier to avoid regenerationin B and also to equalize reception of the signals from A and Brespectively in the vehicle, which is a desirable feature.

Referring in detail to Fig. 1, we have shown one specic arrangement forreceiving the two broadcast waves from the transmittersA and B. For thesake of simplicity A and B batteries are omitted from the diagram ofthis gure. An antenna 10 indicates diagrammatically the means forintercepting the signal waves being broadcast from stations A and B.Coupled to the antenna 10 at 11 is the rst radio receiver X, having anydesired number of stages of radio frequency amplification indicateddiagrammatically by the radio frequency amplifying tube 12. 'Ihe inputcircuit 13 of the amplifier 12 is variably coupled to the antenna at 11,this variable coupling serving as a convenient volume control for energyreproduced in the first receiver. Coupled to the output circuit of theradio frequency amplifier 12 is a mixing tube or detector 14; and to theoutput circuit of this tube 14 is connected any suitable number ofstages of audio frequency amplification indicated diagrammatically byaudio frequency amplifying tube 15, to the output of which there is inturn connected the ear phones 16.

Assuming, for example, that the receiver X is tuned to the frequency ofthe transmitter at B, the signal energy received from B at the antenna10 is amplified at 12; detected at 14; again amplified at 15; and madeaudible at 16. This apparatus thus far described is nothing more than aconventional radio receiving set and the structural details thereof maybe varied in accordance with the well known principles' applied to radioreceivers, without departing from the spirit of this invention.

A second radio receiver Y is variably coupled to the antenna 10 at 21.'Ihis second receiver comprises a suitable number of stages of radiofrequency amplification indicated diagrammatically by the radiofrequency amplifying tube 22, whose input circuit is coupled totheantenna 10 at 23. Since the present receiving apparatus being describedis designed for usev in accordance with that modification of ourinvention inwhich the station 'B is designed to broadcasto'na frequencywhich is an integral multiple of the frequency of the station A, thereceiver Y which is tuned to the lower frequency of the transmitter at Ais provided with a frequency multiplier 24, which is tuned to bring thefrequency of the energy received by the arnplifier 22, up to thefrequency being received in the receiver X. The output circuit of thetube 24 is also coupled to the input of the detector 14.

Here again, as described in connection with receiver X, the receiver Yfunctions as a conventional radio receiving apparatus except, perhaps,for the inclusion of the frequency multiplier, and the energytransmitted from station A is made audible through the receiver Y in theear phones at 16. It will be understood that when the ship carryingreceivers X and Y is stationary with respect to the stations A and B,and both of these stations Vare sending out their continuous waveoscillations of equal frequency, or of frequencies which are integrallyrelated, and further when these continuous wave oscillations transmittedfrom the separate stations are modulated by two separate musical notesas indicated above; then, bothof these musical notes will be indicatedin the ear phones at 16. Since it is preferable that such signalsreceived on the separate receiver X and Y be of equal volume, thecouplings at 11 and 21 are adjusted to realize this equality. We havethus far described an arrangement for receiving the two transmittedcontinuous wave oscillations sent out from stations A and B. Now, inaccordance with the principles of this invention, the move-4 ment of theship carrying the receiver as described above in the common field ofthese two transmitters will produce a beat note, which beat note we havefound, in actual practice, to be below the range of audibility. We havetherefore devised a certain arrangement for indicating this sub-audiblebeat note. While we have disclosed one specinc arrangement forindicating this beat note, it will be clear that many similararrangements will readily suggest themselves to those skilled in the artwithout departing from the spirit and scope of this invention, andtherefore the specific embodiment of the indicating device which wedisclose herein is merely used by way of illustration and that wetherefore do not intend to be limited to details of structure shown.

Referring still to Fig. 1, the low frequency indicating apparatus willnow be described. Coupled to the output of the detector tube is a lowpass filter 30. The cut-off of this lter'is adjusted to prevent any ofthe audiblesignals which are effective in amplifier 15y from reachingthe apparatus which is connected to the present lter. In other words,the apparatus which is now to be described is acted upon only byelectrical waves below the range ofaudibility. The sub-audiblefrequencies which appear in the output circuit of the detector tube 14are not reproduced in the amplifier 15 since they are sub-audible butare passed through the filter 30 to the amplifier tube 31, which tubeboosts the amplitude of these low frequency impulses to a point wherethey completely over-saturate the relay tube 32, into which the tube 31is connected to feed. In the subaudible frequency apparatus wepreferably use resistance coupling as shown. The apparatus is adjustedso that the grid-swing of the tube 32 is so high, that the plate currentof the tube 32 jumps suddenly from zero to saturation value and back atthe impressed frequency of the sub-audible oscillations. In the outputcircuit of the tube 32 there is connected an electromagnetic relay 33,having a tongue 34 which will be jerked from rest position to workposition and back with a very abrupt movement corresponding tovariations in plate current in the tube 32. A spring 35 is attached tothe tongue 34 to impart movement thereto when the relay is de-energized.Connected in the circuit of the tongue 34 is a direct current source 36having a potential of 200 volts, for example. From this source ofpotential the circuit is followed back through a condenser 37 to thecontact point 38. Midway between rest and work position the relay tongue34 passes the contact point 38, thus quickly making and breaking contacttwice for every low frequency beat that is passed through thesub-audible frequency apparatus. Every contact between the tongue 34yand the point 38 momentarily connects the direct current supply 36across the condenser 37 as shown. The condenser 3'7 has a capacitypreferably of one microfarad and the resistance 39 is of 100,000 ohms.

The charge on condenser 37 will leak away through resistance 39 at arate which reduces the initial voltage to 0.368 of its original value in116, Of a second. -The condenser instantaneously charged to E volts willbe discharged during the half period of the beat frequency h, before itreceives a new charge, down to the value 1 V: E( e 2me) where E=initialvoltage e=base of natural logarithms h=beat frequency R=resistance ofleak C=capacity of condenser The average voltage across the condenserduring that time is 1 n z E =,zhEft/0 e mdf where t=time i L :Zh'E-R-C1-e MRC) I It therefore appears that Env, the average voltage acrosscondenser C, is a definite function lof the beat frequency h. For zerobeat. this average voltage is zero. For very high-beat frequencies theterm approaches Fai-Rc and the average voltageis close to the chargingvoltagesE. For a beat frequency of 5 Aper second and theabove values ofE, C, and R, we have:

40 across the condenser 37, and provide resistances 41 and capacities.42 connected'as shown in Fig. 1 in order to retard electrically thevariations of the indicator of meter 40. 'I'he electrical retardation isaccomplished in the 4following manner: K, Referring still to Fig. 1, thecondenser 37 (capacity 1 mfd.) is periodically charged as describedabove by the action of the beat note acting upon the relay at 34, anddischarged through the shunting resistance 39 (R=100;000 ohms). 'I'hemeter 40 is a milliammeter readingfull scale at 0.1 m.A'. Between thecondenser 37 and the meter 40 is connected attenuator of low passcharacter, consisting ofl the two resistances 41 (r=l megohm) and 2 mfd.capacity 42. At the beat note frequency h=5/sec. chosen for example, theimpedance of 42 is 80,000 ohms and the amplitude of fluctuations isreduced 8% (calculated from general filter formula) by. the action ofthe electrical retarder or attenuator.V Of course, the metermay bemagnetically and/or mechanically damped to any desired degree inaddition. The scale of meter 40 may readily be calibrated in frequencyunits. Thusit will be yseen that we have provided a. receiving equipmentadapted to be installed in an airplane, for example, which receiver willrecord directly heterodyne beats produced by movementof the plane in thecommon eld of the transmitters at Afand B.

Above', suitable means have been described for detecting and measuringthe frequency of a heterodyne beat below /sec.

It remains to be proved that such a heterodyne beat is set up in thecommon field of two radio frequency transmitters of equal or harmonicfrequencies, by the motion of a receiver installed in a plane or similarvehicle; and further, that the frequency of such beat note is a knownfunction of and therefore a means for calculating the location anddirection of the vehicle.

'I'he principle is illustrated by thewsketch of Figure 2. A is abroadcasting station sending out waves of a frequency: n/sec. `(=15megacycles) These spread out at the speed of light (C=about 186000miles/sec. At P1 they meet an aeroplane flying towards A at a speed ofV= 100 miles per hour and carrying a receiving set. It is evident, thatthe planewill cross more waves per second, than if itremained immobileat point P1. 'Ihe increased number of encountered waves,

which win 'be tunedvin. and reacted upon the 'receiver, is f i n,=n(`lIn our example, v/c has the small value lEq. 3

The change of frequency is n times v/c, which in our case amounts to2.25 cycles per second.

Now let us assume that the plane, still flying at 100 miles an hour,changes its direction so that it ies at an angle l to the radius vectori A-Pi, as shown in Fig. 3.

The lateral component of ight, v sin l, will not influence the receptionfrequency at all, and

the frequency shift will be due and proportional to the longitudinalcomponent: v cos l. The totalfchange will be Furthermore let us assumethat the broadcast ing frequency is na, but that the receiver contains afrequency multiplier, which brings the de` tector input up to thefrequency nd=lc.n. From vEquation 4 it follows that the broadcast waveis received with the frequency:

n= :1.(1 Coal) After passing the frequency multiplier, it reaches thedetector with the frequency: na-Im='lm 1+ coa l) Itisseen that no matterwhich was the original broadcast wave, the frequency change in thedetector is equal to the detector frequency multiplied by the speed withwhich the plane approaches-the broadcasting station, and divided by thespeed of light.

In Fig. 4 we see the plane P1 flying in the field of two broadcastingstations A and B with speed and direction indicated by vector v. Itapproaches A at the rate of v-cos la, and leaves B at the rate of v-coslb. If both stations are in unison or at harmonic frequencies, broughtto unison `in the common detector, the frequency shift will be I ndy :sl for station A, and nav/c. cos lh for station B.

v This will produce a heterodyne beat of Since the radii Pi-A and B-P1form an angle P, We can. transform Equation 7 into.;

value of h is a function of la alone. It becomes zero for that is when vhas the near vertical direction shown in Fig. 4, which equally dividesthe com- Eq. '4 I plementary angle of p. It becomes a maximum for whichleades to:

l=g+1 1r Eq. 1o

that is, when om hasthe near horizontal direction shown in Fig. 7, whichequally divides the angle P. If we substitute the result of Eq. 10 intoEq. 8, we find:

hmz-12nd-Eros Eq. 11

COS 2.

and p itself.`

The yprocedure for location nding therefore is to make a circular flightand observe direction of flight and beat frequency at the moment ofmaximum beat. Lines drawn at angles P as shown in Fig. `5, on both sidesfrom the direction of maximum beat will point straight towards thebroadcasting stations A and B, respectively. Since the location of A`and B is known, these two beam directions are sufficient data tocalculate the position of lP1 by methods known of spherical trigonometryand used for location finding by the well known directional loop method.

Now let us consider the influence of a winddrift w in the directionindicated in Fig. 6, and pointing at an angle s from the direction ofmaximum beat. We can split the wind force into two components; one ofthem, wm=w cos s points in the direction of maximum beat and influencesour results. The other, w=w sin s points at right angles to wm andaccording to Eq. 9 does not influence the beat frequency at all.

If our plane, under the impact of w, flies a full circle, the navigatorwill observe two maxima of the beat frequency. They occur at the samedirections plus or minus om that they would have at windless flight;only their amounts are different. In the direction aided by the winddrift, the maximum will be P v+w, l `hl=2fld C05 'ib-'- Eq. 12

in the opposite direction:

h2=2nd cos g-V-W Eq. 13

If we form the half sum of these values, we find 2 2nd cos 2 c which isour old value of Equation 11 for the beat note caused by the planealone; it eliminates the wind influence. If we form the half differencehplanz:

0 of 12 and 13, we and .-2114 cos wind-component is found in a seconddirection,

which enables us to calculate the total wind strength and direction.

It is even sufficient, if in addition to the two stations A and B thereis a third station C (preferably not located in a straight line with Aand B), broadcasting on a (third) harmonic of the same fundamentalfrequency as A and B. q

The receiving apparatus has tuning means allowing to receive and beatrst, for example, the frequencies of A and B, then those of A and C.This furnishes a double check on the location findings and twodirectional Wind components: w1 for A and B and w2 for A and C, as shownin Fig. '1.

In Fig. 8 it isshown graphically, how from the wind components w1 and wzwe can nd the total wind vector w and the north and east components wnand we..

Algebraically, we have the following solution:

Multiplying Equation 15 by cos a2 and rearranging:

we sin a1 cos a2=w1 cos a2- wn cos a1 cos a2 Multiplying Equation 16 bycos a1:

subtracting 18h from 18a:

we (sin a1 cos az-cos a1 sin az) Eq. 18a

1.01 COS (l2-1.02 COS al We: W2 cos al-Wl cos a,

Sln az COS al- COS a2 S111 al '=w2 cos ax-wl cos a2 e Sin (agr-a1)Multiplying Equation 15 by sin a2:

Multiplying Equation 16 lby sin a1:

wn cos a2 sin a1=w2 sin a1- we sin a1 sin az subtracting 1'7b fromEquation 17a:

Eq. 17h

wn (cos a1 sin a2,- cos az sin ai) w1 sin az-wz sin az W w1 sin az-wzsin al n cos al sin ag-cos a2 sin a1 w, sin .a2-W2 sin al n Sin (a2-81)Having thus described our invention, we claim;

lDrising in combination,

l. An apparatus of the class described coma rst receiving means, asecond receiving means, means to produce a beat note of a frequencybelow audibility, and means to.y produce a visual indication inaccordance with the frequency of said beat note.

2. An apparatus of the class described comprising in combination, a rstreceiving means,

- a second receiving means, adetector common to both said means, meanscoupled to said detector to produce audible signals received on bothsaid rst -and said second receiving means, means coupled to saiddetector to reproduce a subaudible beat note, and means visually toindicate the frequency of said beat note.-

3. -An apparatus of the class described comprlsing in combination, afirst receiving means, a second receiving means, a detector common toboth said means, means coupled to`said detector to produce audiblesignals received on both said first and said second `receiving means,means coupled to said detector to reproduce a subaudible beat note, .alow pass filter having a cut-oil below audibility interposed .betweensaid last 'mentioned meansl and said detectonand means visually toindicater the fre n'ote.

4. In a device of the character described,

uency of said beat means to indicate the frequency of sub-audibleelectrical oscillations comprising in combination, a relay, a condenser,a source of direct current arranged 'to be connected across saidcondenser periodically under control of said relay, a high resistanceconnected across saidcondenser, and a direct current meter connectedacross said condenser, whereby to indicate the electrical potentialthereacross.

5. In a device of the character described, means to indicate thefrequency of sub-audible electrical oscillations comprising incombination, means to reproduce the said oscillations, a relay connectedto said last mentioned means, a circuit including a condenser and asource of direct current, means operable by said relay to open and closesaid circuit in accordance with the oscillations reproduced, whereby thesaid condenser is charged periodically, means to discharge the condenserin a predetermined time interval, and

means' to indicate the denser.

potential across said con- 6. In ya. device of the character described,

means to indicate the frequency of sub-audible electrical oscillationscomprising in combination, means to reproduce the said oscillations,connectedto said last mentioned means, a including a condenser andasource of direct current, means operable by said relay to open and closesaid circuit in accordance with the oscillations reproduced, whereby thesaid condenser is charged periodically, means to discharge the condenserin a predetermined time interval, means to indicate the potential acrosssaid condenser, and means to attenuatethe response of said lastmentioned means.

7. In a device of the character described, means to indicate thefrequency of subsaudible electrical oscillations comprising incombination, means circuit to reproduce the said oscillations, a relaycona relayl nected to said last mentioned means, a circuit including acondenser and a source of direct current, means operable by said relayto open and close said circuit in accordance with the oscillationsreproduced, whereby the said condenserl is charged periodically, meansto discharge the condenser in a predetermined time interval, means toindicate the potential across said condenser, and means to attenuateelectrically the response of said last mentioned means.

8. A frequency indicating device comprising in combination acircuithaving a condenser and a source of direct, current energy, a movablecontact constructed and arranged to open and close said circuit, a relayoperative under control of the energy whose frequency is to be measuredto move said contact, Ywhereby said condenser is charged periodically inaccordance with the frequency to be indicated, a leak resistanceconnected across said condenser, and means to indicate the potentialacross said condenser.

9. A frequency indicating device comprisingf permit said charge to leakaway at a predetermined rate, and means to measure the potential acrosssaid condenser.

10. 'I'he method of determining the position of a vehicle in the commonfield of two radiating stations of known location, which comprisesmoving said vehicle relatively t`o said stations, producing a beat notebetween signals transmitted from said stations by said movement,determining `the frequency of said beat note, and determining the angleformed by lines drawn from the vehicle to said stations from therelation:

V f v P h,2ndcos 2, where h is the beat frequency, nd is the constantdetector frequency, v is the'driving speed of ythe vehicle, c is thespeed of light, and P is the angle formed by lines drawn from saidvehicle to said stations. 7

11. In the art of radio navigation, the method of determining thelocation of a vehicle in the common field of two stations radiating inunison \by said radiated energy and calculating position from the knownfrequency of beat note in the relation h= 2nd-gees g of the vehicle, cis the speed of light, and P is the angle formed Iby lines drawn fromsaid vehicle to said stations.

WALTER ALBERSHEIM. HARVEY KONHEIM.

which comprises receiving a beat note produced r

